Originally Posted by dee004
Your friend is probably referring to EGR deletes where the old cooler is removed and the stock up pipe is still in place with a plug in the outlet and not being supported by the EGR cooler any longer. It puts stress on the corregations of the up pipe and they may fail causing exhaust leaks and gasses which may enter the truck cab. That's why they sell solid replacement up pipes with no corregations and no need for support with the full EGR delete kits. If the EGR is in place and just blocked off still clamped to the up pipe there isn't an issue.
Even then, the up pipe is supported on top (y pipe) and bottom (exhaust manifold). The outlet to the EGR is very close to the top. The 'corregations' that you mention are the flex joint. Stainless, like many alloys, squirms/moves when it gets heated up. The flex joint is actually what makes it last, instead of cracking at a weak weld joint because it allows a slight bit of movement as the metal heats and cools.